When blood circulation problems, caused by depositions (atheromateous), such as in pelvic, leg or coronary arteries, leading to stenosis, are cured by widening the arteries or breaking up the depositions, or percutaneous transluminal re-canalization, (dilation), the treatment often causes the artery wall to be injured or dissected as a consequence of the medical treatment, (i.e. iatrogenic injuries). Cutaneous flaps hanging from the blood vessel wall into the vessel obstruct the blood flow and may cause vascular occlusion or, in the case of coronary arteries, a heart attack. There are two obvious alternatives to avoid such complications: A balloon catheter may be used to place "stents" (such as wire meshes) into the vessel in order to mechanically stabilize the vessel wall and keep the vessel open. This process, however, makes the occurence of a thrombosis highly probable. An alternative is stated in volume 38, No. 1, January 1990 of Transactions on Microwave Theory and Techniques: "Percutaneous, transluminal microwave balloon angioplasty" by Rosen A. et al. A "hot balloon", such as a mostly multi-luminous balloon catheter, which is equipped with an asymmetric dipole suitable for radiating electromagnetic microwaves, is inserted and supplied with high-frequency energy by a cable inserted into a lumen. This dilatation catheter is inserted into the vessel in a pressure-free state and without being supplied with high-frequency energy and is then supplied with pressure to achieve the desired widening or blasting effect. Subsequently, high-frequency microwave energy is supplied to the dipole in the catheter so that the vessel wall and the direct vicinity of the catheter balloon are heated to a temperature of more than 50.degree. C for a short period. This causes the protein-substance to coagulate so that cutaneous flaps are bonded to the vessel wall.
The microwave high-frequency energy which serves to heat the tissue must be supplied to an antenna dipole in the balloon catheter with as little energy loss as possible, through the coaxial cable assembly of the dilatation catheter. If the attenuation of the coaxial cable is too high, undesirable heat will be generated in the lumen of the catheter in which the coaxial cable assembly is located. This undesirable generation of heat may cause a dangerous coagulation of the blood surrounding the catheter tube. At the same time, however, the cable assembly must be easy to bend in the distal area, in particular when applied in coronary vessels, so that it can be inserted into the vessel concerned even through narrow bends. In the proximal area a certain minimum rigidity is required to insert the cable assembly into the narrow lumen of a catheter and push it further therein. Furthermore, the diameter of the cable assembly should be as small as possible to minimize the diameter required for the lumen.
For this reason, the coaxial cable assemblies used in dilatation catheters comprise a shield consisting of a flat or round conductor, either wound or braided, and covered by a thin metal tube in the proximal area to enhance the rigidity. A disadvantage of this construction, however, is that the metal tube to be pushed over the cable for the sake of rigidity must be relatively thick so that the effective diameter of the cable becomes too large. This reduces the available room for pushing the cable within the lumen. It may even become necessary to use a catheter tube of a larger diameter. Furthermore, such a cable is complex and expensive to produce and not very efficient because a separate manufacturing step must be included to provide for an adequate connection of the tube to the coaxial cable.
Another approach used for cable assemblies in dilatation catheters is to separately produce two cable sections of different rigidity and electrically and mechanically connect them at a common interface with a micro-connector plug. However, this will detract from the electric transmission quality of the cable assembly due to the additional attenuation caused by the interface. Another disadvantage is the complex construction and the high manufacturing costs. In addition, the patient runs the risk of the connection accidentally being severed during the treatment.
There is a need for an improved arrangement with a supply line in the form of a coaxial cable assembly suitable for high-frequency operation for medical applications particularly in hollow organs of the human body.